This invention relates to engines for motorcycles, and more particularly to improved arrangements of the generator and the starting motor located at a side of the engine cylinders.
In a motorcycle in general, an engine and accessories such as a generator, and other electrical parts are mounted in a space defined inside the main frame. A compact main frame is particularly advantageous for designing a motorcycle compact in size. To this end, the accessories should desirably be arranged in a compact manner.
On the other hand, in conventional motorcycles, the generator is usually disposed parallel with the crankshaft which extends transversely of the motorcycle body, so as to make the total width of the engine small as compared with an arrangement in which the generator is disposed at an end of the crankshaft in axial alignment. In such conventional arrangement, the crankshaft, a mainshaft adapted to be driven by the crankshaft via a clutch, and a countershaft having gears meshing with multispeed transmission gears mounted on the mainshaft are arranged on a substantially horizontal common plane. As a consequence, the clutch casing, which accommodates a primary reduction driven gear and a clutch, both having large sizes, clutch has its upper surface projected considerably far above the upper surfaces of the mainshaft casing and the countershaft casing accommodating the mainshaft and the countershaft, respectively, leaving rather a small space between the upper surface of the clutch casing and the carburetor of the engine arranged above these casings.
Owing to this spatial limitation, in the type where the generator is arranged on the upper surfaces of the mainshaft casing and the countershaft casing, usually a starting motor is arranged rearwardly of the generator. However, according to this arrangement, if a compact main frame has a portion thereof disposed close to a rear side of the engine, it is hard or impossible to mount an engine fitting hanger at the rear side of the engine when mounting the engine onto the main frame, since the starting motor is rearwardly projected toward the main frame. Also, as for the engine per se, it is desirable to reduce the axial size or length of same as well as the transverse size or width, for compacting the main frame.
Further, according to the above-mentioned conventional arrangement of the generator and the starting motor, the generator casing, the starting motor casing and mounting frames therefor are inevitably fabricated separately, requiring a large number of man-hours for fabrication and assemblage due to many component parts, which results in degradated productivity as well as increased weight of the engine.
Still further, if the generator is arranged close to the engine cylinders or to the starting motor, particularly for compacting the main frame, its temperature can be elevated due to heat radiated by the engine cylinders or the starting motor, or due to its own heat. This requires use of component parts having high heat resistance in the generator. Therefore, the generator should desirably be provided with a cooling means.